1999-03-26 04:00:00 PDT RICHMOND -- A fiery explosion at the Chevron refinery in Richmond yesterday afternoon sent flames and thick black smoke billowing into the air, forcing thousands of residents to shut themselves indoors to stay away from the fearsome fumes.

Three Chevron emergency response team workers were injured. As the cloud mushroomed over the East Bay, hundreds of residents ventured out to area hospitals for treatment of possible ill effects from the fumes. By last night, more than 1,200 had showed up at emergency rooms, complaining of breathing difficulties and eye irritations.

The 2:28 p.m. explosion happened in the heat exchanger of the Isomax plant, which produces gasoline and airline fuel.

Chevron officials said they did not know what had caused the fire but expressed relief that there were no injuries among the 10 workers normally assigned to the area. The plant is where the hydrocracking process converts heavy crude oil into light fuels.

"It's certainly a blessing that nobody was injured," said Terry Swartz, a Chevron spokesman.

Some of those usually assigned to the area were in a blast- resistant control center, located about a quarter-mile from the site of the explosion.

Flames from the fire were extinguished by 4:30 p.m., but firefighters stayed on through the evening, spraying thousands of gallons of water on the machinery.

Once the unit was sufficiently cooled, workers planned to go in and shut off a valve that could keep the fire supplied with fuel should it reignite.

Swartz said the explosion created "a very hot fire, and when you have burning liquid, it's unpredictable. We're throwing everything we have at it."

Chevron's fire department of 60 firefighters and paramedics were joined by up to 50 firefighters from the Richmond Fire Department in battling the blaze.

The explosion and fire occurred on the north side of the 2,500-acre refinery, where the Chevron plant processes 240,000 barrels of crude oil every day, Swartz said. Chevron officials said it was not clear how the shutting-down of the fire-damaged unit would affect production of fuel.

The winds sent a huge plume of smoke -- and odor -- drifting up to the Carquinez Bridge near Crockett. When the winds shifted, it drifted back toward the Richmond-San Rafael Bridge and on to the El Cerrito and Berkeley waterfront area.

It was the noxious odor that sent people streaming to hospitals and prompted the State Bar of California to hand out flyers cautioning people against unscrupulous lawyers trying to cash in on the event.

Among those seeking medical help was Tamara Sexton, 31, who is three months pregnant and was worried that the smoke might have caused injuries to her unborn child.

"I'm in my first trimester, which is more dangerous," the Richmond resident said. "That's when the baby starts forming. Of course I'm worried. I don't even know what the toxin was."

The main problem was the potential release of sulfur compounds, particularly hydrogen sulfide and sulfur dioxide, said air quality district spokesman Terry Lee.

"But we have a monitoring truck out there, and it can't detect either of those compounds," she said.

It was the second major refinery explosion in Contra Costa County in the past five weeks. On February 23, a fire in Tosco's Avon refinery killed four workers and seriously injured one. The last big explosion at the Chevron refinery was in March 1994, when toxic gas blew out of flares when some of the refinery's instruments failed.

"This is a very frustrating experience," Miller said by phone last night from Washington. "We've had these explosions and these terribly tragic events. It's a hazardous industry, no question about that. But each and every time, you have to go in and find out what went wrong. . . .

"The community is forced to go through this on a periodic basis," he said. "So, do we have a culture of safety in these refineries? I know they say they do, but it raises a question. Clearly, the refineries have an interest in having a good safety record, for a whole host of reasons, but we continue to have these events take place."

Contra Costa County Health Services spokeswoman Elinor Blake said her agency issued a "shelter in place" warning, asking residents to close and lock their windows and doors, and close fireplace flues, in order to keep smoke and fumes from homes.

The "all clear" signal was given at 8:30 p.m.

Residents said there was a 20-minute delay from the time they heard the explosion and saw the smoke to the time sirens from the county's emergency warning system went off. There are five sirens in Richmond.

County officials said that there was a delay in the alerting system and that they were investigating the problem.

An automatic-dialing phone system was in working order, county officials said, but it, too, suffered delays in operation yesterday. The system dials the phones of homes in immediately affected areas and a recorded message instructs residents to remain indoors and turn off air- conditioners.

BART temporarily shut down its Richmond station, but it was reopened at 5:30 p.m. Cars heading toward Interstate 580 from Interstate 80 were diverted east on I-80 toward Sacramento for a time.

The accident happened about a mile from the nearest residential area. The fire and its smoke could be seen shooting straight up throughout the area, from Marin County to Walnut Creek.

At the eastern edge of the refinery, two men hurriedly loaded car parts on a truck as they got ready to get out of the smoke-filled neighborhood.

"It kind of rumbled and the ground shook, and there was, like, a sonic boom," said Ronald Bugg.

"A giant mushroom of smoke exploded into the sky in this great big ball of fire and kept burning for 15 minutes," Williams said. "There were at least three small explosions in the next few minutes after the first one. It was as if it was feeding on itself."

Three refinery employees suffered injuries in the effort to contain the fire after the blast occurred, according to Marielle Boortz, spokeswoman for the Chevron refinery, who issued a company apology for the event.

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One suffered a sprained back and the second suffered from heat exhaustion. Both received medical attention, though Boortz was not aware if they had been hospitalized late yesterday. The third employee suffered "stomach distress."

The refinery officials received word quickly that all employees were accounted for, and no one was injured directly in the blast, Boortz said.

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